In computer storage systems (also referred to herein as storage subsystems), disk partitioning and logical volume management are used to manage physical storage devices such as hard disk drives. In disk partitioning, a single storage device is divided into multiple logical storage units referred to as partitions, thereby treating one physical storage device as if it were multiple disks. Logical volume management provides a method of allocating space on mass-storage devices that is more flexible than conventional partitioning schemes. In particular, a volume manager can concatenate, stripe together or otherwise combine regions (a region is a sequence of bytes having a specific length, typically one megabyte) into larger virtual regions that administrators can re-size or move, potentially without interrupting system use.
To manage a given volume, a volume map that defines the relationship between a given logical volume's regions and physical regions (also known as blocks) on the physical storage device. For example, International Business Machines' (IBM) Advanced Interactive eXecutive™ (AIX™) operating system typically stores the volume map in a Volume Group Descriptor Area (VGDA). The VGDA is typically stored at the beginning of each physical storage device, and contains information that describes the relationship (i.e., mapping) between the volumes and the physical storage devices of an AIX™ system. In operation, an AIX™ system can read the VGDA from the physical storage device, and determine what physical storage devices and logical volumes are available to the system.